The invention relates to a self-centering releaser for a pressed-type friction clutch and particularly a releaser having a sliding sleeve of synthetic plastics material on which a grooved ball bearing is radially movably guided.
From German Patent No. 2,240,715 a self-centering releaser for a pressed-type motor vehicle friction clutch is known, the sliding sleeve of which consists of synthetic plastics material and comprises an annular flange formed thereon integrally and protruding to the exterior radially of the axis of the sleeve. On the side facing the clutch the annular flange forms a flat abutment face on which an outer race ring of a deep-groove ball bearing is directly supported. The ball bearing lies with its inner race ring against diaphragm spring tongues of the clutch and is freely movable at least in the radial direction in relation to the sliding sleeve and its annular flange. In this case the ball bearing is seated in a retaining fitting secured to the external circumference of the annular flange. A spring braced in between the outer race ring and the retaining fitting presses the outer race ring against the abutment face. On actuation of the clutch the ball bearing lying through the inner race ring against the diaphragm spring, is centered radially against the retaining force of the spring.
Sliding sleeves of synthetic plastics material are ordinarily produced by the injection molding method. This can have the consequence that the abutment face of the annular flange is not completely flat, since the synthetic plastics surface can sink in during casting. Furthermore the synthetic plastics material under pressure loading by the outer race ring tends to creep, which reduces the life of the releaser. Finally two sealing rings arranged axially on both sides of the path of circulation of the balls are necessary for sealing off the ball bearing of the known releaser. The sealing rings are seated in grooves on the internal circumference of the outer race ring and seal off against axial shoulders of the inner race ring. Such sealing rings require additional machining of the outer race ring and the inner race ring, increasing the production expense of the ball bearing.
It is the problem of the invention to lengthen the life of a self-centering releaser of the kind as explained above.